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Chronological List of LLMs: 2018 to 2026 Model Evolution

Chronological index of 50+ key LLMs from BERT and GPT-1 to o1 and DeepSeek-R1, with sizes and dates linked to sources; unconfirmed figures are flagged.

Published Updated 19 min readBy ,
On this page
  1. In short
  2. Overview
  3. Phase 1 (2018–20)
  4. Phase 2 (2021)
  5. Phase 3 (2022)
  6. Phase 4 (2023)
  7. Phase 5 (2024–26)
  8. Evolution
  9. FAQ
  10. Sources

In short

A Large Language Model (LLM) is a neural network based on transformer architectures, pre-trained on massive corpora using self-supervised learning, and fine-tuned for generation, reasoning, and tool use. Since the introduction of the Transformer in 2017, LLM development has progressed through five distinct architectural phases: foundational pretraining (2018–2020), dense scaling (2021), compute-optimal alignment (2022), the open-weight revolution (2023), and native test-time reasoning with sparse mixture-of-experts (2024 onward).

#Executive summary and architectural eras

  1. Foundational pre-training (2018–2020): Shift from recurrent architectures (LSTMs) to self-attention. Emergence of masked language modeling (BERT) and autoregressive sequence prediction (GPT-1, GPT-2, GPT-3).
  2. Dense Scaling & Compute Frontiers (2021): Massive scale-ups (Megatron-Turing 530B, Gopher 280B) and initial explorations of sparse Mixture of Experts (GLaM).
  3. Compute-Optimal Scaling & RLHF (2022): The Chinchilla paper recalibrates token-to-parameter ratios (70B parameters, about 4x the training data of the 280B Gopher at similar compute); Reinforcement Learning from Human Feedback (RLHF) makes ChatGPT a consumer breakout.
  4. The Open-Weight Ecosystem (2023): Meta's Llama series, Mistral's sliding-window architectures, and low-rank adaptation democratize fine-tuning on commodity silicon.
  5. Native Reasoning, MLA & Test-Time Compute (2024–2026): Transition to multi-million token context windows, inference-time chain-of-thought search (OpenAI o1), and high-efficiency Multi-head Latent Attention (DeepSeek-V3/R1).

Scope: the tables stop at January 2025. Later releases (for example the Claude 5.x, GPT-6 and Gemini 4 families) are covered in our 2026 model guide. On 2026-11-03 we opened the arXiv abstract page, developer blog or Hugging Face model card linked in Sources for every row with a paper or vendor link, and checked the date, developer, parameter count and, where the page states them, context length and licence. Where a page gave a different or narrower figure, the row was corrected or softened (for example HyperCLOVA, GPT-NeoX, Cerebras-GPT and DeepSeek-LLM now give the paper date, because we did not open a page stating an earlier release date). Where a developer page does not state a figure, the cell says so. Four limits apply. (1) OpenAI's own pages return an access error to our fetch tool. For GPT-1 (11 Jun 2018), GPT-2 (14 Feb 2019, with the 1.5B size and the staged release) and ChatGPT (30 Nov 2022, RLHF) we read Wayback Machine captures of the OpenAI pages (captured 8 May 2024, 8 May 2024 and 2 May 2024), which show the publication date and text. For GPT-4o (13 May 2024) and o1 (12 Sep 2024) the Wayback copies could not be read; the Wayback index lists captures dated 13 May 2024 and 12 Sep 2024, which shows the pages existed by those days, and the day-level dates otherwise rest on excerpts seen in search results. (2) The GPT-1 parameter count comes from the Hugging Face model card (0.1B); the often-quoted 117M is not stated on any page we opened. (3) The Access Type column and one-line impact descriptions were checked only where a linked page states them; for Claude 2.0 (Jul 2023), Megatron-Turing NLG's October 2021 announcement, Ernie, GLaM and similar entries only the paper date was confirmed. (4) Jurassic, Yi and Nemotron are not in these tables. Exact day-level dates are given only where a page we opened states them. "Undisclosed" means the developer has not published the figure.


#Phase 1: Foundational Transformers & Architecture Emergence (2018–2020)

Model Release Date Organization Parameters Key Architectural Feature / Impact Access Type
GPT-1 Jun 2018 OpenAI About 0.1B (Hugging Face card lists 0.1B; the commonly cited 117M is not stated there) Established generative pre-training + discriminative fine-tuning Open weights
BERT Oct 2018 Google BERT-Large about 336M (Hugging Face card; often rounded to 340M) Bidirectional masked language modeling (MLM) and Next Sentence Prediction Open source
GPT-2 Feb 2019 OpenAI 1.5B Demonstrated zero-shot task transfer via parameter scaling; 1.5B model first withheld, released in stages Open weights (later release)
XLNet Jun 2019 Google / CMU Similar to BERT-Large (~340M) Permutation language modeling overcoming BERT pretrain-finetune mismatch Open source
RoBERTa Jul 2019 Meta / UW 355M Hyperparameter and dataset optimization over BERT baseline Open source
T5 Oct 2019 Google Up to 11B Unified Text-to-Text Transfer Transformer framework Open source
GPT-3 May 2020 OpenAI 175B Established emergent in-context few-shot learning at scale Proprietary API

#Phase 2: Dense Scaling, Conversational Seeds & Compute Boundaries (2021)

Model Release Date Organization Parameters Key Architectural Feature / Impact Access Type
GPT-Neo Mar 2021 EleutherAI 2.7B Community-driven, open-source GPT-3 replication Open weights
HyperCLOVA 2021 (paper Sep 2021) Naver 82B Non-English foundational model optimized for the Korean language Commercial API
GPT-J mid-2021 EleutherAI 6B Dense open alternative implementing Rotary Position Embeddings (RoPE) Open weights (Apache 2.0)
Megatron-Turing NLG Paper Jan 2022 Microsoft / NVIDIA 530B Giant transformer training utilizing DeepSpeed & Megatron pipeline parallelism Research
Ernie 3.0 Titan Dec 2021 Baidu Up to 260B Knowledge-enhanced multi-task pre-training model API / Research
GLaM Dec 2021 Google 1.2T (MoE) Sparsely activated Mixture-of-Experts; reduced carbon and training compute Research
Gopher Dec 2021 DeepMind 280B Extensive analysis of capabilities and failure modes across model sizes Research

#Phase 3: Compute-Optimal Scaling Laws & Dialogue Alignment (2022)

Model Release Date Organization Parameters Key Architectural Feature / Impact Access Type
LaMDA Jan 2022 (paper) Google Up to 137B Transformer specialized for human-like multi-turn dialogue Not stated in the paper abstract
GPT-NeoX Paper Apr 2022 EleutherAI 20B Open autoregressive model; the paper describes a 20-billion-parameter model Open weights (Apache 2.0 per its Hugging Face card)
Chinchilla Mar 2022 DeepMind 70B Established data-to-parameter scaling laws (4x more tokens vs. parameter size) Research
PaLM Apr 2022 Google 540B Pathways architecture scaled across 6,144 TPU v4 chips; strong results on multi-step reasoning tasks Research
OPT May 2022 Meta AI 125M–175B Suite of decoder-only models; OPT-175B comparable to GPT-3 with about one-seventh the carbon footprint (per the paper) Shared with researchers
YaLM 100B 2022 Yandex 100B Pre-trained bilingual (Russian/English) foundational model Open weights
Minerva Jun 2022 Google Not stated in abstract Specialized for solving complex STEM, calculus, and scientific challenges Research
BLOOM Jul 2022 (Hugging Face card estimate: 11 Jul 2022; paper Nov 2022) BigScience / HF 176B Collaborative open-science multilingual model: 46 natural and 13 programming languages Open weights (BigScience RAIL licence 1.0)
Galactica Nov 2022 Meta AI 120B Scientific information processor trained on academic literature and papers Research
ChatGPT (GPT-3.5) Nov 2022 OpenAI Undisclosed Mainstream consumer breakout via Reinforcement Learning from Human Feedback Web / API

#Phase 4: The Open-Weight Revolution & Instruction Tuning (2023)

Model Release Date Organization Parameters Key Architectural Feature / Impact Access Type
Llama Feb 2023 Meta AI 7B–65B High performance on modest parameter budgets; kickstarted open research Research weights
Alpaca Mar 2023 Stanford 7B Fine-tuned from LLaMA 7B on 52K instruction demonstrations; research use only, weights not released at launch Open research (code and data)
GPT-4 Mar 2023 OpenAI Undisclosed Multimodal model; technical report withholds architecture and size Proprietary API
Cerebras-GPT Apr 2023 (paper) Cerebras 111M–13B Models trained following Chinchilla scaling rules on a Cerebras Wafer-Scale Cluster Not stated in the paper abstract
Falcon 2023 (paper Nov 2023) TII (UAE) 7B / 40B / 180B Falcon-180B trained on over 3.5T tokens; Hugging Face card lists a 2048-token sequence length Open weights (Falcon-180B under the TII licence, gated)
BloombergGPT Mar 2023 (paper) Bloomberg L.P. 50B Domain-specific LLM; 363B-token dataset built from Bloomberg's data sources plus 345B general-purpose tokens Not stated in the paper abstract
Vicuna Mar 2023 LMSYS 13B Chat model tuned on about 70K user-shared ShareGPT conversations; non-commercial use Open weights (non-commercial)
PaLM 2 May 2023 Google Not disclosed in report Heavily multilingual, optimized for reasoning, coding, and translation API
Phi-1 / Phi-2 Jun–Dec 2023 Microsoft 1.3B / 2.7B Proven efficiency using curated synthetic "Textbooks Are All You Need" Open weights
Llama 2 Jul 2023 Meta AI 7B, 13B, 70B Open-weight release with a licence that permits commercial use under Meta's terms Open weights
Claude 2 / 2.1 Jul–Nov 2023 Anthropic Undisclosed Claude 2.1 (21 Nov 2023) offered a 200K-token window and, per Anthropic, about half the false statements of Claude 2.0 Proprietary API
Mistral 7B Sep 2023 Mistral AI 7.3B Sliding Window Attention (SWA) and Grouped-Query Attention (GQA); announced 27 Sep 2023 Apache 2.0
DeepSeek-LLM Paper Jan 2024 DeepSeek 7B / 67B Base and chat models; the paper reports a 2-trillion-token pre-training dataset Open weights
Grok-1 Mar 2024 (open release) xAI 314B (MoE) Mixture-of-experts with about 25% of weights active per token; custom JAX and Rust training stack; Apache 2.0 Open weights
Gemini 1.0 Dec 2023 Google DeepMind Nano, Pro, Ultra Built natively multimodal across text, audio, image, and video modalities Proprietary API
Mixtral 8x7B Dec 2023 (paper Jan 2024) Mistral AI About 47B total (13B active) Sparse MoE, 2 of 8 experts per token; 32k-token context (Mistral announcement, 11 Dec 2023); per its paper matches or outperforms Llama 2 70B and GPT-3.5 on the benchmarks evaluated Apache 2.0

#Phase 5: Massive Context, SLMs & Test-Time Reasoning (2024–2026)

Model Release Date Organization Parameters Key Architectural Feature / Impact Access Type
OLMo Feb 2024 (paper 1 Feb 2024) AI2 1B and 7B (Hugging Face cards) Released with open training data and training and evaluation code Fully open (Apache 2.0 per the 7B card)
Gemma / Gemma 2 21 Feb 2024 / mid-2024 (paper 31 Jul 2024) Google DeepMind 2B and 7B (Gemma); 2B, 9B and 27B (Gemma 2) Lightweight open models based on Gemini research and technology Open weights
Gemini 1.5 Feb 2024 (paper Mar 2024) Google DeepMind Flash / Pro Long-context multimodal model; announced 15 Feb 2024 with a 1M-token window in limited preview (128K standard); the paper reports near-perfect retrieval in tests up to at least 10M tokens Proprietary API
Claude 3 / 3.5 Mar–Jun 2024 Anthropic Haiku, Sonnet, Opus (sizes undisclosed) Claude 3 family of three tiers announced 4 Mar 2024; Claude 3.5 Sonnet published 21 Jun 2024 Proprietary API
DBRX Mar 2024 Databricks 132B total (36B active) Fine-grained MoE: 16 experts, 4 chosen per input; 27 Mar 2024; up to 32K-token context Open weights (licence not named on the announcement page)
Command R+ Apr 2024 Cohere Not stated in announcement Launched first on Microsoft Azure; aimed at enterprise retrieval and tool use API
Llama 3 & 3.1 8B and 70B on 18 Apr 2024; paper 31 Jul 2024 Meta AI 8B, 70B, 405B Llama 3 was trained on 8,192-token sequences; the Llama 3.1 paper describes a dense 405B Transformer with a context window up to 128K tokens Open weights (Meta's licence terms)
Phi-3 / Phi-4 Apr–Dec 2024 Microsoft 3.8B–14B Small language models (phi-3-mini 3.8B, paper 22 Apr 2024; Phi-4 14B, 12 Dec 2024, 16K context) Open weights (Phi-4 under MIT per its Hugging Face card)
GPT-4o / mini May–Jul 2024 OpenAI Undisclosed End-to-end omnimodal engine handling unified text, vision, and natural audio Proprietary API
Qwen 2.5 Sep 2024 (report Dec 2024) Alibaba Cloud 0.5B to 72B (open models) Released 19 Sep 2024; pretraining data expanded from 7T to 18T tokens; up to 128K-token input Open weights (Apache 2.0 except the 3B and 72B variants, per the Qwen blog)
OpenAI o1 Sep 2024 OpenAI Undisclosed Reasoning model that spends more time thinking before it responds Proprietary API
DeepSeek-V3 / R1 Dec 2024–Jan 2025 DeepSeek 671B total (37B active) V3 (paper 27 Dec 2024; 14.8T tokens; 128K context) uses Multi-head Latent Attention (MLA) and DeepSeekMoE; R1 (paper 22 Jan 2025) trained with reinforcement learning for reasoning Open weights (R1 under MIT; V3 code under MIT, V3 weights under DeepSeek's model licence, which permits commercial use)
Gemini 2.0 Flash Dec 2024 Google DeepMind Undisclosed Fast Gemini 2.0 model with multimodal input and tool use Proprietary API

#Architectural evolution: what changed over seven years

#1. From Dense Scaling to Sparse Mixture-of-Experts (MoE)

Early foundation models (GPT-3, PaLM, OPT) are dense: every parameter is used for every token. Contemporary open models (Mixtral, DBRX, DeepSeek-V3) route each token through a router so only a subset of parameters is active (for example 37B of 671B in DeepSeek-V3), which lowers compute per token compared with a dense model of the same total size.

#2. Attention Mechanisms: From Quadratic MHA to FlashAttention and MLA

Standard Multi-Head Attention (MHA) compute scales quadratically O(N2)O(N^2) with sequence length NN, which limited early context windows (GPT-3 used 2,048 tokens). Two advances reduced the cost:

  • FlashAttention (Dao et al., 2022): An exact attention algorithm that reduces reads and writes between GPU high-bandwidth memory and on-chip SRAM (arXiv:2205.14135).
  • Multi-Head Latent Attention (MLA, DeepSeek-V2, 2024): Compresses the key-value (KV) cache into a low-rank latent representation to cut inference memory; DeepSeek-V3 adopts it (arXiv:2412.19437).

#3. From Pretraining Scaling to Test-Time Compute Scaling

Historically, model capability was tied to compute spent during pretraining (Kaplan et al., 2020; Hoffmann et al., 2022). With OpenAI o1 and DeepSeek-R1, labs also scaled compute at inference: the models spend extra time generating reasoning before they answer. DeepSeek-R1's paper describes eliciting this reasoning with reinforcement learning.


#Frequently asked questions

#What was the first large language model?

There is no single agreed answer, because "large" is relative and neural language models predate transformers. GPT-1 (OpenAI, June 2018, about 0.1B parameters per its Hugging Face card) and BERT (Google, October 2018, BERT-Large at about 336M parameters per its Hugging Face card) are the usual starting points for the transformer era. This list begins there for that reason.

#What is the difference between open-weight and open-source models?

Open-weight releases publish the trained parameters so you can download and run the model, but often not the training data or full training pipeline. Fully open projects such as AI2's OLMo release open training data and training and evaluation code alongside the model. Licences differ, so read the terms before commercial use.

#Why did parameter counts stop growing so fast after 2022?

The Chinchilla paper (Hoffmann et al., 2022) showed that a 70B model trained on about four times more data than the 280B Gopher could do better at similar compute, so labs shifted toward more training tokens per parameter. Sparse mixture-of-experts designs also let total size grow while active parameters stay lower.

#What is a mixture-of-experts model?

A mixture-of-experts (MoE) model contains many expert sub-networks and a router that picks a few for each token. Mixtral activates 2 of 8 experts per token (about 13B of 47B parameters), and DeepSeek-V3 activates 37B of 671B. Compute per token is lower than for a dense model of the same total size.

#Which models count as reasoning models?

OpenAI's o1 (September 2024) and DeepSeek-R1 (January 2025) are the two covered here. Both spend additional computation generating reasoning before answering. DeepSeek-R1's paper, published in Nature in 2025, describes training this behaviour with reinforcement learning, and its weights are openly available.

#Why are some parameter counts marked undisclosed?

Several developers, including OpenAI for GPT-4 (whose report says it contains no details on architecture, including model size) and Google for PaLM 2, do not state model sizes in their technical reports. Figures circulating elsewhere are estimates or leaks, so this list shows "Undisclosed" rather than repeat them.


#Sources

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